1. Technical Field
The present invention relates to an anode active material for lithium secondary batteries, a preparation method thereof and a lithium secondary battery including the same. More particularly, the present invention relates to an anode active material for lithium secondary batteries, which includes a silicon-containing core provided on the surface thereof with silicon nanoparticles, a preparation method thereof and a lithium secondary battery including the same.
2. Description of the Related Art
Generally, a lithium secondary battery includes: an anode made of a carbon material or a lithium-metal alloy; a cathode made of a lithium-metal oxide; and an electrolyte including an organic solvent and a lithium salt dissolved in the organic solvent. Particularly, as an anode active material constituting an anode of a lithium secondary battery, a lithium metal had initially been used. However, since lithium has a problem of low reversibility and is considered unsafe, currently, a carbon material is being generally used as an anode active material for a lithium secondary battery. Although a carbon material is inferior to a lithium metal in capacity, it has a small volume change and excellent reversibility, and is advantageous in terms of price.
However, with the increase in the usage of lithium secondary batteries, demands for large-capacity lithium secondary battery have gradually increased, and thus a large-capacity anode active material that can replace a carbon material has been required. In order to meet such a requirement, attempts to use a metal (for example, silicon (Si)), having a larger charge-discharge capacity than a carbon material and capable of being electrochemically alloyed together with lithium, as an anode active material have been conducted.
However, such as metal-based anode active material is problematic in that its volume is greatly changed during charging-discharging, and thus an active material layer is cracked. Therefore, a rechargeable battery including this metal-based anode active material is also problematic in that its capacity rapidly decreases during a charge-discharge cycle, and its lifecycle also decreases, and thus it is not commercially available.
However, when a non-carbon material, such as SiO, is used as an anode active material, there are advantages in that high-capacity characteristics can be realized, and volume expansion with respect to Si can be controlled, compared to when a carbon material is used. Thus, research into non-carbon materials has been variously conducted. However, when a non-carbon material is used, there is a disadvantage in that by-products created by the reaction of Li and O cause an irreversible reaction, thus lowering the initial efficiency of a rechargeable battery.
Therefore, in order to overcome the above problems, research into SiOx has been actively conducted. For example, Korean Patent Application Publication No. 2012-7011002 discloses an anode active material for lithium secondary batteries, wherein SiOx is used as an anode active material. However, this anode active material is problematic in that charge-discharge cycle characteristics cannot be sufficiently improved, and in that the x value of SiOx cannot be easily adjusted by a conventional synthesis method.